Disk drives are capable of storing large amounts of digital data in a relatively small area. Disk drives store information on one or more recording media, which conventionally take the form of circular storage disks (e.g. media) having a plurality of concentric circular recording tracks. A typical disk drive has one or more disks for storing information. This information is written to and read from the disks using read/write heads mounted on actuator arms that are moved from track to track across the surfaces of the disks by an actuator mechanism.
Generally, the disks are mounted on a spindle that is turned by a spindle motor to pass the surfaces of the disks under the read/write heads. The spindle motor generally includes a shaft mounted on a base plate and a hub, to which the spindle is attached, having a sleeve into which the shaft is inserted. Permanent magnets attached to the hub interact with a stator winding on the base plate to rotate the hub relative to the shaft. In order to facilitate rotation, one or more bearings are usually disposed between the hub and the shaft.
Over the years, storage density has tended to increase, and the size of the storage system has tended to decrease. This trend has lead to greater precision and lower tolerance in the manufacturing and operating of magnetic storage disks. For example, to achieve increased storage densities, the read/write heads must be placed increasingly close to the surface of the storage disk. This proximity requires that the disk rotate substantially in a single plane.
From the foregoing discussion, it can be seen that the bearing assembly that supports the storage disk is of critical importance. One bearing design is a fluid dynamic bearing. In a fluid dynamic bearing, a lubricating fluid such as air or liquid provides a bearing surface between a fixed member of the housing and a rotating member of the disk hub. In addition to air, typical lubricants include gas, oil, or other fluids. The relatively rotating members may comprise bearing surfaces with fluid dynamic grooves formed on the members themselves. Fluid dynamic bearings spread the bearing surface over a large surface area, as opposed to a ball bearing assembly, which comprises a series of point interfaces. The use of fluid in the interface area imparts damping effects to the bearing, which helps to reduce non-repeatable run-out. Thus, fluid dynamic bearings are an advantageous bearing system.
However, fluid dynamic bearing designs are susceptible to problems caused by manufacturing tolerance variations in bearing (and bearing groove) geometry. These problems include variations in pressure produced in the journal bearing and a possible entrapment of air bubbles in the fluid (where the fluid is a liquid) itself. Both of the stated problems may be avoided by providing a fluid dynamic bearing with a fluid re-circulation path to an external environment.
Therefore, a need exists for a fluid dynamic bearing design that utilizes capillary seals combined with fluid re-circulation. Furthermore, a bearing design that can do so while eliminating any air that enters the fluid bearing system is desirable to prolong motor life.